To replace the ankle joint, an endoprosthesis is known comprising a component to be connected to the ankle bone, a component to be connected to the shin bone, and an intermediate part (DE-U-88 12 806, brochure “LINK S.T.A.R. Totale Sprunggelenk-prothese [H. Kofoed] from Waldemar Link (GmbH & Co.), Hamburg). The ankle bone component and the intermediate part interact via slide surfaces which permit flexion and extension in the sagittal plane. The shin bone component and the intermediate part form interacting slide surfaces which permit a rotation about the vertical axis of the endoprosthesis. They can be of a plane design in order to permit compensating movements in the antero-posterior (AP) direction and latero-medial (LM) direction. Stabilization is afforded by the natural ligament apparatus.
In the known prosthesis, the top and bottom slide surfaces of the intermediate part are oriented parallel to one another in the frontal plane because the prosthetic replacement of the joint is not intended to result in a change in direction. However, it has been found that, after surgery, the collateral and medial ligaments of the joint often have different tensioning, which can cause problems. This may be due to irregularities of the anatomy or to the fact that the operating surgeon has chosen an unfavorable orientation of the resection surface provided on the shin bone for connection to the prosthesis.